Along with the technology development and the increased demand for mobile devices, the demand for secondary batteries as energy sources is rapidly increasing. Among the secondary batteries, a lithium secondary battery having a high energy density and voltage, a long cycle life, and a low discharge rate is commercialized and widely used.
The lithium secondary battery is configured so that a non-aqueous electrolyte containing a lithium salt is impregnated in an electrode assembly in which a porous separator is interposed between a positive electrode and a negative electrode. The positive electrode and the negative electrode are respectively fabricated by applying slurry containing an electrode active material on an electrode current collector thereof, followed by a rolling process.
While the positive electrode is being prepared, the slurry is pressed toward the current collector in the rolling process. In this process, a portion of the surface of the positive electrode current collector is dug concavely by positive electrode active material particles contained in the slurry, and accordingly a contact area between the positive electrode mixture layer and the positive electrode current collector increases, thereby improving the adhesion between the positive electrode mixture layer and the positive electrode current collector.
This positive electrode active material is made using secondary particles. However, since the secondary particles collapse during the electrode fabricating process to have a shape of a primary particle, the surface of the positive electrode current collector is not dug, and thus the contact area between the positive electrode mixture layer and the positive electrode current collector is not increased, thereby lowering the adhesion to some degree.
Also, if a polymer binder is used in a large amount in order to improve the adhesion between the positive electrode mixture layer and the positive electrode current collector, the amount of the positive electrode active material is relatively decreased, which may deteriorate the battery capacity or increase the resistance.